Method of treating motion sickness

ABSTRACT

Certain anticonvulsant drugs have been found to be effective in the treatment of motion sickness. These compounds have the structure: ##STR1## wherein R 1 , R 2  and R 3  are H, aliphatic or aromatic groups; 
     B is --C═O or --CH 2  --; 
     n&#39; is 0 or 1; 
     n&#34; is 0 or 1; and 
     X is ##STR2##  with the further proviso that when n&#39; is 1, n&#34; is also 1, and their non-toxic, pharmaceutically acceptable acid addition salts.

BACKGROUND OF THE INVENTION

This invention relates to the prevention or treatment of motionsickness. More particularly, the present invention is directed topreventing motion sickness by the use of a certain class ofanticonvulsants.

Traditional motion sickness therapies rely predominantly upon drugs inthe antihistaminic and anticholinergic drugs classes. See Money, K. E.,Motion Sickness, Physiological Reviews, 1970, 50(1);1-39; Wood, C. D.,Graybiel, A., Theory of Antimotion Sickness Drug Mechanisms, AerospaceMed., 1972, 43(3):249-252; and Wood, C. D., Manno, J. E., Wood, M. J.,Manno, B. R., Redetzki, H. M., Mechanisms of Antimotion Sickness Drugs,Aviat. Space Environ. Med., 1987, 58(9, Suppl.):A262-5. Examples of suchdrugs are promethazine, scopolamine dimenhydrinate and cyclazine. Theseare sometimes combined with a sympathomimetic agent such as ephedrine oramphetamine to enhance their action and reduce the side effects orlethargy and drowsiness that often accompanies the use of these drugs.Other traditional side effects of drugs presently used in the preventionof motion sickness include blurred vision, dizziness, dry mouth andsedation. In addition, therapy with the present day antimotion sicknessdrugs whether used alone or in combination with other drugs is less thanoptimal

It is an object of the present invention to prevent or treat motionsickness by the use of drugs found to be far more effective thananti-motion sickness agents presently employed without theaforementioned side effects that frequently accompany these drugs.

Another object of the invention is to prevent or treat motion sicknesswith agents which do not require use of additional enhancing agents orside-effect reducing agents.

SUMMARY OF THE INVENTION

These and other objects are obtained by administering to a patientsusceptible to or suffering from motion sickness an anti-motion sicknesseffective amount of at least one compound having the structure: ##STR3##wherein R₁, R₂ and R₃ are H, aliphatic or aromatic groups;

B is --C═O or --CH₂ --;

n' is O or 1;

n" is O or 1; and

X is ##STR4## with the further proviso that when n' is 1, n" is also 1,and their non-toxic, pharmaceutically acceptable acid addition salts.

R₁, R₂ and R₃ can be similar of dissimilar and are often a mixture ofhydrogen, an aromatic group and an aliphatic group. Suitable aromaticgroups for the R₁, R₂ and R₃ groups include aryl groups of 6 to 12carbon atoms, preferably phenyl. Suitable aliphatic groups for the R₁,R₂ and R₃ groups include alkyl groups of 1 to 5 carbon atoms.

The anti-motion sickness compounds particularly preferred are phanytoin,ethotoin and primidone.

Recent studies of laboratory induced motion sickness in human subjectshave revealed novel electroencephalographic changes accompanying thedisorder. These EEG changes, similar to those sometimes seen in partialseizure, are characterized by a pattern of high voltage, low frequency(below 0.5 Hertz) oscillations.

The observation of these electroencephalographic changes was coupledwith consideration of the symptoms sometimes seen in partial seizure.These symptoms include autonomic dysfunctions like cardiovascular andrespiratory irregularities, epigastric sensations and gastrointestinalhypermotility; features nearly synonymous with motion sickness.Consequently, drug treatment with agents in the anticonvulsant classthat would stabilize neuronal membranes to excessive stimulation and/orreduce polysynaptic responses seemed indicated. Further investigationled to the discovery that the administration of effective amounts of theabove-identified anticonvulsants prevent or alleviate motion sickness.

The term "motion sickness" as used in this specification and appendedclaims includes airsickness, seasickness, space motion sickness, groundvehicle sickness, e.g.: car sickness, flight simulator sickness andearth sickness DeMarquement (the symptoms of motion illness on returningto earth or solid ground after flying in space, water-borne travel,etc.).

DETAILED DESCRIPTION OF THE INVENTION

Examples of suitable acids for the non-toxic, pharmaceuticallyacceptable acid addition salts are inorganic acids such as hydrochloricacid, hydrobromic acid, nitric acid, sulfuric acid and phosphoric acidand organic acids such as formic acid, acetic acid, propionic acid,benzoic acid, maleic acid, fumaric acid, succinic acid, tartatic acid,citric acid, oxalic acid, glyoxylic acid, aspartic acid, alkanesulfonicacids such as methanesulfonic acid and ethanesulfonic acid, arylsulfonicacids such as benezenesulfonic acid and p-toluene sulfonic acid andarylcarboxylic acids.

Examples of suitable excipients or pharmaceutical carriers are talc,arabic gum, lactose, starch, magnesium stearate, cacaco butter, aqueousand non-aqueous vehicles, fatty bodies of animal or vegetable origin,paraffinic derivatives, glycols, diverse wetting agents, dispersants oremulsifiers and preservatives.

The active compounds of the invention are administered to a patientsusceptible to motion sickness which can be any warm-blooded animal,including man, either before or after the onset of motion sicknesssymptoms. The administration can be effected orally, intramuscularly orintravenously. The usual daily dosage will depend on the subjecttreated, the particular compound administered and the method ofadministration. Generally, the doses used will parallel those used inthe treatment of seizures which are dosages that provide a blood levelwithin the range from about 4 to 100 micrograms. For example, forphenytoin, a blood level in the range of about 10 to 20 micrograms permilliliter is satisfactory. The dose necessary to achieve this bloodlevel concentration would be, on average, 1 gram in several divideddoses as a loading dose, and 300 milligrams per day thereafter.

The following Example further illustrates the invention but is not to beconstrued as limiting the invention in any respect.

EXAMPLE

Seven healthy young adult males (25 to 37 years of age) participated.Informed consent was obtained from all subjects.

All subjects' susceptibilities to motion sickness, according to theirwritten responses to motion experience/sickness questionnaires, wereunremarkable. All subjects were also, weeks before the formalexperiment, evaluated for their response to coriolis stimulation byusing the same head motion protocol and rotational speed which would beemployed in the trials to follow. Their time course of symptomdevelopment and time to nausea during this preliminary evaluation werecompared to those recorded during the subsequent placebo trials in orderto determine if any adaption was occurring over the course of thetrials.

The coriolis motion stimulus was conventionally generated by performingvoluntary, random, full range-of-motion right/up, left/up, down/up headmotions at ten second intervals while rotating at a constant 14, 16, 18,20, or 22 rpm in the yaw axis. The rotational rate was chosen with thegoal of providing a motion intensity which would induce emesis withinapproximately 10 to 15 minutes. Increasing individual susceptibility anda corresponding slower rotational rate was subjectively assignedaccording to an individual's history (frequency and intensity) of car,sea, air, etc. sickness symptomatology reported in the motionexperience/sickness questionnaire. More than ten separate physiologicparameters were simultaneously recorded through the experiment. Theseincluded respiratory rate and volume, and bipolar temporal and midlineelectroencephalogram (acquired with subdermal electrodes and amplifierswith a low frequency response extending to 0.2 Hertz).

The subject would regularly report hs subjective symptomatology. Datacollection would continue through frank sickness and emesis or until thesubject chose to end the experiment.

A double blind placebo controlled crossover experimental technique wasemployed. At least one week separated each subject's placebo andtreatment trials. A total of approximately 1 to 1.4 grams (15 milligramsper kilogram of bodyweight) of phenytoin or placebo, in 5 or 6 equaldoses, was taken orally over a 20 hour period prior to the experiment(coriolis stimulation began approximately four hours after the finaldose). This dose and schedule was chosen to achieve a blood level in thetraditional therapeutic range of 10 to 20 micrograms per milliliter andto obviate any rare side effects associated with acute administration.(Note: In one aborted experiment, a subject reported acute nauseaassociated with the loading dose administration. This was the specificside effect it was essential to avoid.) A physical examination wasperformed prior to each experimental trial to characterize balance,reflexes, coordination, performance, as well as nystagmus and any otherside effects.

RESULTS

In all trials, physical exam failed to reveal any evidence ofneurological symptoms, signs or compromise. Subjects denied the presenceof side effects such as double vision, dizziness, tremor, ataxia,nausea, (or as with the more traditional treatment) dry mouth, blurredvision, sedation, etc. Four subjects did, however, report a sense (infact accurately) that they knew when they had taken the activetreatment. Of those four, two reported the sensation of a very slight"light-headedness", and two a sensation of stimulation or alertness.

In each case during the placebo trails, the subject's time to nausea waswithin ten percent of the time observed in the preliminary coriolisstimulation evaluation. (This implies that adaption was not asignificant factor in determining the tolerance to motion in theexperimental trials.)

Electroencephalographic changes were also observed in 5 of the 7subjects in this study. (This is similar to my experience in my priorunpublished preliminary research where 14 of 24 symptomatic untreatedsubjects developed high voltage temporofrontal delta wave activity.)During the phenytoin trials, this slow wave activity was delayed byseveral minutes in two subjects compared to their placebo trials. In twoother subjects, the electroencephalographic changes were delayed untilthe onset, after prolonged stimulation, of motion sicknesssymptomatology. In one of the two subjects who was immune to any motioninduced symptomatic response, the electroencephalographic delta wavechanges failed to appear.

Tolerance to motion sickness with phenytoin therapy, measured by thenumber of head motions required to induce emesis, was extended insubject #1 by a factor of 6.2. Subject #2 experienced an extension oftolerance of 6.1 times. Subjects #3, #4 and #7 had extensions of 3.1,9.5 and 4 times, respectively. Subjects #5 and #6, while reaching emesiswith placebo in 13 and 38 minutes respectively, remained asymptomaticfor more than an hour during their phenytoin trials before they chose toend the experiments (see FIG. 1).

The ratio of the duration of symptom free time with phenytoin versusplacebo was even more pronounced. A mean of a factor of 11.9 wasobtained (see FIG. 2).

It is claimed:
 1. A method of treating motion sickness comprisingadministering to a patient susceptible to or suffering from motionsickness, an anti-motion sickness effective amount of a compoundselected from the group consisting of diphenylhydantoin, ethotoin andprimidone, and their non-toxic, pharamaceutically acceptable acidaddition salt.
 2. A method according to claim 1 wherein the compound isdiphenylhydantoin.
 3. A method according to claim 1 wherein the compoundis ethotoin.
 4. A method according to claim 1 wherein the compound isprimidone.